Category: Ducts

Mastic duct sealer can be applied to the non-metallic part of ductboard. Mastic is a high-quality sealant that is often used in HVAC systems to seal joints and seams against air leakage. It is designed to adhere to a wide variety of materials, including the fiberglass and foil-faced surfaces of ductboard.

Here’s how to apply it:

1. Clean the Surface: Make sure the surface of the ductboard is clean and dry. Remove any dust, dirt, or grease that could prevent the mastic from adhering properly.

2. Apply Mastic: Using a brush or gloved hand, apply a generous layer of mastic to the ductboard. Make sure to cover all seams and joints.

3. Let it Dry: Allow the mastic to dry completely. This could take several hours or even overnight, depending on the thickness of the application and the temperature and humidity of the environment.

4. Inspect the Seal: Once the mastic has dried, check to make sure the seal is complete. If there are any gaps or cracks, apply another layer of mastic and let it dry.

Remember, always follow the manufacturer’s instructions when using mastic or any other sealant.

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you can apply the mastic to both the 2″ side of the ductboard and the side of the furnace before joining them together. However, you need to make sure it’s applied carefully and evenly to get a good seal.

Here’s a simple step-by-step guide:

1. Clean the Surfaces: Make sure both surfaces (the ductboard and the furnace) are clean and free of dust, dirt or grease.

2. Apply the Mastic: Use a brush to apply a thick, even layer of mastic on both surfaces. Make sure you cover the entire surface area that will be joined.

3. Join the Surfaces: Press the ductboard against the furnace firmly. This ensures that the mastic spreads out evenly and fills any gaps or irregularities between the two surfaces.

4. Secure the Joint: If necessary, you can use duct tape or mechanical fasteners to hold the ductboard in place while the mastic dries. Do not rely on these for the seal – they just provide extra support.

5. Let it Dry: Leave the mastic to dry completely. This can take several hours or even overnight, depending on the conditions.

6. Check the Seal: Once the mastic is dry, check the seal. If there are any gaps or cracks, apply another layer of mastic.

Remember, always follow the manufacturer’s instructions when using mastic. And keep in mind that mastic should not be used in areas where it will be exposed to high heat, such as near the heat exchanger or flue pipe of a furnace. 

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While mastic is an excellent sealing material, it’s not typically used as a structural component. The primary function of a duct collar is to provide a secure, mechanical connection between the duct and the furnace, while the mastic provides an airtight seal.

Without a duct collar, the mastic alone may not be sufficient to hold the duct in place and withstand the pressure differences that occur during the operation of the HVAC system, especially in the long term.

So while you might be able to get away without using a duct collar in the short term, it is highly recommended to use one for a long-lasting and secure connection. After the collar is installed, mastic can then be applied around the connection to ensure an airtight seal.

According to North Carolina building codes, there are specific requirements for constructing duct collars when building a large ductboard supply duct into the furnace:

1. All connections, including the duct collar, must be sealed with water-based duct mastic1. This is critical for meeting the new North Carolina Energy Conservation Code (NCECC) requirements.
2. Tape can be used during installation, but should not be relied upon as the primary method of air sealing ductwork1. Mastic should be applied over the tape to ensure airtightness.
3. The duct collar should be properly sized and well-sealed where it meets the air handler1. This is particularly important due to the large size of plenums, as poor connections at the air handler can lead to significant leaks.
4. When connecting the ductboard to metal components like the furnace, a metal collar or sleeve should be used to ensure a secure and airtight connection4.
5. The duct collar must be constructed to meet the pressure class requirements of the system4. Each size in a pressure class has minimum specifications for joints and reinforcements.
6. Proper support for the duct collar and adjacent ductwork is required. Metal straps with a minimum width of 1 inch (25 mm) and equivalent to or heavier gauge than the duct material should be used for support8.
7. The duct collar should be designed to allow for proper airflow and minimize pressure drop in the system4.

Remember to consult the specific North Carolina Mechanical Code and SMACNA guidelines for detailed requirements and best practices when constructing duct collars and connections.

Red Devil 0841DX F-Seal 181 Fiber Reinforced Water Based Duct Sealant is indeed considered a duct mastic and offers several advantages over regular water-based mastic:

1. Fiber reinforcement: F-Seal 181 contains fibers that enhance its sealing strength and workability, making it more durable and effective for sealing duct joints12.
2. UL listings: It is UL 181A-M and B-M listed, indicating it meets strict standards for use with both rigid fiberglass ductwork and flexible air ducts14.
3. Versatility: F-Seal 181 is suitable for various HVAC applications, including metal ductwork, fiberglass duct board, and flex duct, both indoors and outdoors24.
4. Performance: It exceeds all SMACNA pressure and sealing classes, providing excellent adhesion and flexibility14.
5. Additional benefits: F-Seal 181 offers mold and mildew resistance, low VOC content, and contributes to LEED EQ Credit 4.124.

While regular water-based mastic can be effective, F-Seal 181’s fiber reinforcement and specific formulation for HVAC applications make it a superior choice for many duct sealing tasks. Its fast drying time, excellent adhesion, and ability to seal high, medium, and low-pressure HVAC duct systems further set it apart from standard mastics45

Red Devil 0841DX F-Seal 181 Fiber Reinforced Water Based Duct Sealant offers several environmental benefits:

1. Low VOC content: The product has low volatile organic compound emissions, which contributes to better indoor air quality68.
2. LEED compliance: It is LEED EQ 4.1 compliant, supporting green building practices and sustainability initiatives8.
3. Water-based formula: Being water-based, it reduces the use of harmful solvents and is more environmentally friendly compared to solvent-based alternatives6.
4. Improved energy efficiency: By effectively sealing HVAC duct systems, it helps reduce energy waste and improves overall system efficiency6.
5. Durability: The fiber-reinforced formula provides long-lasting performance, reducing the need for frequent reapplication and minimizing waste6.
6. Versatility: It can be used on various duct materials, including metal, fiberglass duct board, and flex duct, both indoors and outdoors, reducing the need for multiple specialized products68.
7. Mold and mildew resistance: This feature helps maintain a healthier indoor environment and extends the life of the ductwork1.

These environmental benefits align with Red Devil’s commitment to meeting product demands while helping to preserve the environment and complying with environmental health and safety regulations1.

If mastic is used to seal an HVAC joint properly, there is generally no need to apply tape and then mastic over the tape. Mastic alone is considered sufficient for sealing duct joints when applied correctly12. Here’s why:

1. Mastic is more durable and long-lasting than tape, often lasting up to 20 years or longer3.
2. It creates a flexible, airtight seal that can withstand temperature changes and vibrations1.
3. For small gaps (less than 1/4 inch), mastic can be applied directly to the joint without additional reinforcement4.

However, there are some situations where using both tape and mastic might be beneficial:

1. For medium gaps (1/4-3/4 inch), you can first apply fiberglass mesh tape over the gap, then cover it with mastic4.
2. When sealing flexible duct connections, some professionals recommend using high-quality duct tape first, then sealing with mastic for added protection2.
3. In cases where immediate temporary sealing is needed before mastic can fully cure, tape might be used as an initial layer4.

Remember, when applying mastic:

• Clean the surface thoroughly before application5.
• Apply a generous amount, ensuring complete coverage of the joint or seam16.
• Allow 24-48 hours for the mastic to fully cure3.

In most cases, properly applied mastic alone is sufficient for sealing HVAC joints without the need for additional taping.